1. Field of the Invention
The present invention relates to the routing of data within communications networks, including but not confined to networks such as the Internet and particularly, but not exclusively, to a method of routing data directed to a mobile node. The mobile node may be a mobile host, such as a portable computer, or it may be a router which is responsible for the mobility of one or more entire networks, for example, the mobile data network within an aircraft. In either case, the mobile node may change its point of attachment from one network or sub-network to another.
2. Related Art
The routing of data around the diverse networks which make up the Internet is based on a protocol known as the Internet Protocol (IP). Data is transferred in the form of data units known as IP datagrams between points in the Internet specified by IP addresses. The detailed specification of IP is available in a “Request for Comments” document, RFC 791, maintained by the Internet Engineering Task Force (IETF). RFC documents are widely available on the Internet.
The current version of IP, known as IPv4, does not itself support mobility, but a protocol entitled “IP Mobility Support”, commonly referred to as Mobile IP, has been designed to enhance IPv4 to support mobility. This protocol is described in document RFC 2002, available as detailed above. The next generation of IP (IPv6) is being specifically designed to deal with the mobility requirement.
IPv4 assumes that a node's IP address uniquely identifies the node's fixed point of attachment to the Internet. If the node is transferred to a different point, it can only be contacted by allocating it a new IP address. Mobile IP, however, enables a mobile node, such as a laptop or palmtop computer, to send and receive IP datagrams over the Internet regardless of the physical location at which it is connected to the Internet and without changing its IP address.
However, a mobile node may find itself in many different environments, attached to data networks of varying types that serve different purposes.
A mobile node may be linked to a network by a variety of different media, some suited to transmission of high volume data, some not. Some networks may themselves not be able to support higher data rates. A mobile user attached to a particular network may wish to receive data in a particular format, for example to receive web-page data in abridged form, without pictures, or an e-mail in the form of a voice message. In a particular example, a “Wireless Application Protocol” (WAP) has been specially developed for the bandwidth constraints and screen size associated with cellular telephony. If a user is currently using a network suited to that technology, it would be convenient to have the data transmitted in that form. However, if the user is connected to a higher bandwidth system, he may wish to receive the data in a less abbreviated form more appropriate to that other network.
There may also be special associations between the home and visited networks of the transmitter and sender of the data, for example functionality only available if both parties are working on (visiting) the same network, or a service level agreement made between the network operators.